# 4.1.10. Delt: delta line model¶

The delta line model is a simple model for an infinitely narrow emission line.

The spectrum is given by:

where is the photon energy in keV, the photon flux in units of , is the line energy of the spectral line (in keV) and is the line normalisation (in units of ). The total line flux is simply given by .

To ease the use for dispersive spectrometers (gratings) there is an option to define the wavelength instead of the energy as the basic parameter. The parameter type determines which case applies: type=0 (default) corresponding to energy, type=1 corresponding to wavelength units.

Warning

When changing from energy to wavelength units, take care about the frozen/thawn status of the line centroid and FWHM.

Warning

You need to do a “calc” or “fit” command to get an update of the wavelength (for type=0) or energy (type=1).

The parameters of the model are:

norm : Normalisation , in units of . Default value: 1.
e : The line energy in keV. Default value: 6.4 keV.
type : The type: 0 for energy units, 1 for wavelength units.
w : The line wavelength in Å. Default value: 20 Å.